/*
示例：
document.write("GPS: 39.933676862706776,116.35608315379092<br />");
var arr2 = GPS.gcj_encrypt(39.933676862706776, 116.35608315379092);
document.write("中国:" + arr2['lat']+","+arr2['lon']+'<br />');
var arr3 = GPS.gcj_decrypt_exact(arr2['lat'], arr2['lon']);
document.write('逆算:' + arr3['lat']+","+arr3['lon']+' 需要和第一行相似（目前是小数点后9位相等）');
*/
var GPS = {
  PI: 3.14159265358979324,
  x_pi: (3.14159265358979324 * 3000.0) / 180.0,
  delta: function(lat, lon) {
    // Krasovsky 1940
    //
    // a = 6378245.0, 1/f = 298.3
    // b = a * (1 - f)
    // ee = (a^2 - b^2) / a^2;
    var a = 6378245.0
    var ee = 0.00669342162296594323
    var dLat = this.transformLat(lon - 105.0, lat - 35.0)
    var dLon = this.transformLon(lon - 105.0, lat - 35.0)
    var radLat = (lat / 180.0) * this.PI
    var magic = Math.sin(radLat)
    magic = 1 - ee * magic * magic
    var sqrtMagic = Math.sqrt(magic)
    dLat = (dLat * 180.0) / (((a * (1 - ee)) / (magic * sqrtMagic)) * this.PI)
    dLon = (dLon * 180.0) / ((a / sqrtMagic) * Math.cos(radLat) * this.PI)
    return {
      lat: dLat,
      lon: dLon,
    }
  },
  //WGS-84 to GCJ-02
  gcj_encrypt: function(wgsLat, wgsLon) {
    if (this.outOfChina(wgsLat, wgsLon))
      return {
        lat: wgsLat,
        lon: wgsLon,
      }

    var d = this.delta(wgsLat, wgsLon)
    return {
      lat: wgsLat + d.lat,
      lon: wgsLon + d.lon,
    }
  },
  //GCJ-02 to WGS-84 粗略
  gcj_decrypt: function(gcjLat, gcjLon) {
    if (this.outOfChina(gcjLat, gcjLon))
      return {
        lat: gcjLat,
        lon: gcjLon,
      }

    var d = this.delta(gcjLat, gcjLon)
    return {
      lat: gcjLat - d.lat,
      lon: gcjLon - d.lon,
    }
  },
  //GCJ-02 to WGS-84 精确(二分极限法)
  // var threshold = 0.000000001; 目前设置的是精确到小数点后9位，这个值越小，越精确，但是javascript中，浮点运算本身就不太精确，九位在GPS里也偏差不大了
  gcj_decrypt_exact: function(gcjLat, gcjLon) {
    var initDelta = 0.01
    var threshold = 0.000000001
    var dLat = initDelta,
      dLon = initDelta
    var mLat = gcjLat - dLat,
      mLon = gcjLon - dLon
    var pLat = gcjLat + dLat,
      pLon = gcjLon + dLon
    var wgsLat,
      wgsLon,
      i = 0
    while (1) {
      wgsLat = (mLat + pLat) / 2
      wgsLon = (mLon + pLon) / 2
      var tmp = this.gcj_encrypt(wgsLat, wgsLon)
      dLat = tmp.lat - gcjLat
      dLon = tmp.lon - gcjLon
      if (Math.abs(dLat) < threshold && Math.abs(dLon) < threshold) break

      if (dLat > 0) pLat = wgsLat
      else mLat = wgsLat
      if (dLon > 0) pLon = wgsLon
      else mLon = wgsLon

      if (++i > 10000) break
    }
    //console.log(i);
    return {
      lat: wgsLat,
      lon: wgsLon,
    }
  },
  //GCJ-02 to BD-09
  bd_encrypt: function(gcjLat, gcjLon) {
    var x = gcjLon,
      y = gcjLat
    var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * this.x_pi)
    var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * this.x_pi)
    bdLon = z * Math.cos(theta) + 0.0065
    bdLat = z * Math.sin(theta) + 0.006
    return {
      lat: bdLat,
      lon: bdLon,
    }
  },
  //BD-09 to GCJ-02
  bd_decrypt: function(bdLat, bdLon) {
    var x = bdLon - 0.0065,
      y = bdLat - 0.006
    var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * this.x_pi)
    var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * this.x_pi)
    var gcjLon = z * Math.cos(theta)
    var gcjLat = z * Math.sin(theta)
    return {
      lat: gcjLat,
      lon: gcjLon,
    }
  },
  // 求距离
  distance: function(latA, logA, latB, logB) {
    var earthR = 6371000
    var x =
      Math.cos((latA * Math.PI) / 180) *
      Math.cos((latB * Math.PI) / 180) *
      Math.cos(((logA - logB) * Math.PI) / 180)
    var y = Math.sin((latA * Math.PI) / 180) * Math.sin((latB * Math.PI) / 180)
    var s = x + y
    if (s > 1) s = 1
    if (s < -1) s = -1
    var alpha = Math.acos(s)
    var distance = alpha * earthR
    return distance
  },
  outOfChina: function(lat, lon) {
    if (lon < 72.004 || lon > 137.8347) return true
    if (lat < 0.8293 || lat > 55.8271) return true
    return false
  },
  transformLat: function(x, y) {
    var ret = -100.0 +
      2.0 * x +
      3.0 * y +
      0.2 * y * y +
      0.1 * x * y +
      0.2 * Math.sqrt(Math.abs(x))
    ret +=
      ((20.0 * Math.sin(6.0 * x * this.PI) +
          20.0 * Math.sin(2.0 * x * this.PI)) *
        2.0) /
      3.0
    ret +=
      ((20.0 * Math.sin(y * this.PI) + 40.0 * Math.sin((y / 3.0) * this.PI)) *
        2.0) /
      3.0
    ret +=
      ((160.0 * Math.sin((y / 12.0) * this.PI) +
          320 * Math.sin((y * this.PI) / 30.0)) *
        2.0) /
      3.0
    return ret
  },
  transformLon: function(x, y) {
    var ret =
      300.0 +
      x +
      2.0 * y +
      0.1 * x * x +
      0.1 * x * y +
      0.1 * Math.sqrt(Math.abs(x))
    ret +=
      ((20.0 * Math.sin(6.0 * x * this.PI) +
          20.0 * Math.sin(2.0 * x * this.PI)) *
        2.0) /
      3.0
    ret +=
      ((20.0 * Math.sin(x * this.PI) + 40.0 * Math.sin((x / 3.0) * this.PI)) *
        2.0) /
      3.0
    ret +=
      ((150.0 * Math.sin((x / 12.0) * this.PI) +
          300.0 * Math.sin((x / 30.0) * this.PI)) *
        2.0) /
      3.0
    return ret
  },
}